Field of the Invention
The present invention relates to a composite oxide catalyst used for a vapor-phase catalytic oxidation or vapor-phase catalytic ammoxidation reaction of propane or isobutane and a method for producing the composite oxide catalyst, and a method for producing an unsaturated acid or unsaturated nitrile using the composite oxide catalyst.
Description of the Related Art
It is conventionally known that a method for subjecting propylene or isobutylene to a vapor-phase catalytic oxidation or vapor-phase catalytic ammoxidation reaction to produce corresponding unsaturated carboxylic acid or unsaturated nitrile. In recent years, attention has been directed to a method for subjecting propane or isobutane instead of propylene or isobutylene to a vapor-phase catalytic oxidation or vapor-phase catalytic ammoxidation to produce corresponding unsaturated carboxylic acid or unsaturated nitrile.
For this reason, as a catalyst of vapor-phase catalytic ammoxidation of propane or isobutane, a variety of oxide catalysts have been proposed.
The ammoxidation catalyst is usually a metal oxide obtained by mixing, drying, and calcining molybdenum, vanadium, antimony, niobium, and the like when necessary. The composition of metals contained in the metal oxide has been examined in a variety of composition ratios because the composition ratio directly influences the ability of the catalyst. Further, recently, it is found that physical properties of the metal oxide that cannot be expressed only by the composition ratio also influence the ability of the catalyst.
For example, Patent Literature 1 describes a metal oxide containing molybdenum, vanadium, antimony, and niobium, and having a reduction rate of 8 to 12%, and a specific surface area of 5 to 30 m2/g.
Patent Literature 2 describes production of a protruding substance that inhibits fluidity on the surface of an ammoxidation catalyst. According to Patent Literature 2, by removing the substance from the surface of the catalyst, a yield of a target product can be maintained, and an unsaturated acid and an unsaturated nitrile can be produced.
Patent Literature 1: International Publication WO 2004-108278
Patent Literature 2: Japanese Patent Application Laid-Open No. 2007-216212